This invention relates to blood leak detectors, and more particularly to blood leak detectors that are useful in hemodialysis systems.
During the course of hemodialysis treatment, blood is circulated through an artificial kidney in close proximity to a dialysate comprising a prepared chemical solution designed to cleanse the blood of organic wastes and excess fluids and to equalize the chemical balance of the blood. These results are accomplished utilizing a membrane which separates the blood from the dialysate and acts as a medium of transfer. The membrane is constructed to permit the required fluid flow therethrough while preventing the loss of whole blood into the dialysate. A persistent problem in hemodialysis treatment is the possibility of either blood leaking through or complete rupture of the membrane of the artificial kidney. Any such occurrence results in blood loss from the patient being treated with consequences which range from insignificant to extremely serious. It is therefore critical to monitor the dialysate flowing from an artificial kidney to detect the presence of blood therein and to actuate an alarm if more than a predetermined amount of blood is detected in the effluent dialysate.
Almost all hemodialysis systems heretofore provided have been equipped with blood leak detectors. However, the blood leak detectors heretofore available have exhibited numerous problems. For example, effluent dialysate is characterized by both liquids and gas bubbles flowing with the liquids. In prior blood leak detectors, these gas bubbles have frequently caused false actuations of the alarm system. Another problem that has characterized prior blood leak detectors is the rapid contamination thereof by waste materials. Another disadvantage has been the failure of blood leak detectors to recognize the optical characteristics of blood and to take advantage thereof to provide a system that is highly reliable in operation.
The present invention comprises a blood leak detector which overcomes the foregoing and other disadvantages which have long since characterized the prior art. In accordance with the broader aspects of the invention, a screen is utilized to remove gas bubbles from the flowing liquid of the dialysate. By this means false triggerings of the alarm of the system are completely eliminated. A beam of green light is directed through the liquid of the dialysate, and a photosensitive device responsive to green light is utilized to generate output signals indicative of the opacity of the liquid. Due to the optical characteristics of blood, the use of a beam of green light to test the opacity of the dialysate liquid has been found to substantially increase the reliability of the system. The screen and the light beam generating and detecting systems are mounted in a housing and are positioned substantially above the bottom thereof. Foreign materials may therefore be accumulated in the bottom of the housing without interfering with the operation of the system.
In accordance with more specific aspects of the invention, the green light beam generating system and the light beam detecting system are mounted in cylindrical plugs which extend into the opposite ends of the housing. The screen comprises a 70 micron stainless steel screen which is wrapped around the cylindrical plugs to form a cylindrical configuration. The screen is provided with a slot at the top thereof to permit gases to escape from the interior of the cylindrical configuration of the screen. The screen is positioned directly in the path of dialysate flow through the housing and functions to permit liquid to pass through the green light beam while preventing bubbles from entering the light beam and thereby generating false output signals from the light sensitive device.
The blood leak detector of the present invention is preferably utilized in a blood leak detector system including a reference blood leak detector which receives fresh dialysate flowing to an artificial kidney and a monitor blood leak detector which receives effluent dialysate flowing from the artificial kidney. The outputs from the reference blood leak detector and the monitor blood leak detector are directed to a comparator circuit which functions to compare the two outputs. Whenever the output of the monitor blood leak detector goes off normal as compared with the output of the reference blood leak detector, the comparator circuit actuates an alarm which indicates that blood has been detected in the effluent dialysate flowing from the artificial kidney.